Hello Sharron – Ann here…
The L is 'Generally' not a finger size as the manufacturer wouldn't know if the item was to be re-sized anytime in the future, but have you checked the size anyway?
It may just be a model design identification mark, which together with the ACC combined to be the Maker or Store hallmark anyway.
The crown and the 22 carat marks are as you suggest, together with the Birmingham assay office (well done) but you have missed a couple of important points.
Firstly we need to know the type of FONT the letter 'P' is formed from. While you say it is uppercase, you didn't mention if it was in 'Old English' or Italic etc.
The second is the SHAPE of the stamp. Is is square, oval, rectangular with the corners cut off etc.
These are the parts that most people forget.
However you do give us a hint as to the age, so at least we can begin to look around that time frame, as Hallmarks change in 'Blocks' of about 20 – 25 years.
If the STAMP is squarish with a squiggly bit on the bottom and the date letter 'p' is lowercase (might look to you as uppercase though) then the Birmingham date is indeed 1914. While if it is in uppercase – the date would be 1939.
So you see now why we have to take ALL of the stamp marks together, in order to pin it down.
HTH – Ann